1. Technical Field
The present invention relates to an inflatable vehicle occupant restraint, such as an air bag, and more particularly to an initiator assembly for igniting gas generating material to inflate the restraint.
2. Description of the Prior Art
It is well known to protect a vehicle occupant using an air bag which is inflated when the vehicle encounters sudden deceleration, such as in a collision. The air bag is inflated when the deceleration is of a magnitude sufficient to require air bag inflation. The air bag restrains movement of the vehicle occupant during the collision. The air bag is typically inflated by gas generated by ignition of gas generating material. The gas generating material is contained in an air bag inflator.
The air bag inflator commonly has an initiator which includes an electrically actuatable igniter to ignite the gas generating material. U.S. Pat. No. 5,131,679, assigned to the assignee of the present application, discloses an air bag inflator which comprises an electrically actuatable igniter. The inflator has a housing for containing the gas generating material. The housing includes a housing cover. The igniter is connected to the housing cover by a plastic molded body part which holds the igniter inside the inflator housing in proximity to the gas generating material. The cover is a metal part which is welded to the inflator housing. During assembly, the igniter and inflator cover are positioned in a die, in a spaced-apart relationship. The plastic material of the body part, in a molten state, is injected into the die. The plastic hardens and adheres to the cover and igniter. The plastic molded body part, in addition to connecting the igniter to the housing cover, also functions to seal the igniter within the inflator housing to prevent leakage of gas from the inflator following ignition of the gas generating material.
The injection molding step is a difficult manufacturing operation. It has to take place at relatively low pressures and temperatures because pyrotechnic material is contained within the igniter. This limits the materials and procedures which are available to form a good plastic-to-metal bond.
It is known to provide a plastic body part which is not injection molded around other component parts of the igniter and the inflator housing. In this design, the igniter is connected to an inflator housing part by an annular plastic collar which is snap-attached to the inflator housing part and to the igniter. The inflator housing part has an annular recess. The collar has an inwardly facing annular ridge which snaps into the inflator housing part recess. The igniter is provided with a similar recess, and the collar has a second annular inwardly facing ridge which snaps into the igniter recess as well. The collar thus holds the igniter and the inflator housing parts together. Component parts of the design have facing surfaces which are separated by a pair of O-ring seals. The O-ring seals seal the igniter within the inflator and prevent leakage of gas from the inflator following ignition of gas generating material within the inflator.
This known design has many component parts, including the two O-rings, adding to the cost of manufacture of the inflator. In addition, the collar has to be of a rigid plastic material to securely engage the recesses of the igniter and the inflator housing part.